This invention relates to the use of a pulsed laser to excite a piezoelectric transducer as a method of nondestructive characterization of test materials. Conventional ultrasonic piezoelectric (PZ) transducers are excited to emit stress waves by sending a large, short, electrical potential across the piezoelectric transducer. Through the piezoelectric effect, this potential causes stresses in the transducer which are then transmitted out of the PZ transducer into another material in which, in one embodiment, ultrasonic stress waves are induced. In conventional technology, the large electrical signal required to generate the ultrasonic waves causes several problems in the design and construction of the PZ transducer and associated electronics, including limited dynamic range, poor control of the signal shape, and a poor resolution of echoes which return to the PZ transducer a short time after the pulse. PZ transducers have been used in the prior art to generate ultrasonic waves for a microscope having a plurality of imaging modes permitting a two-dimensional scanning of a test sample. In U.S. Pat. No. 4,510,810, issued Apr. 16, 1985, a PZ transducer both transmits and receives ultrasonic waves induced by an RF electric pulse signal.
U.S. Pat. No. 4,641,529, issued Feb. 10, 1987, discloses a pipeline inspection apparatus for detection of corrosion pit defects which avoids the necessity of a liquid or solid-contact coupling. A single PZ transducer transmits and receives ultrasonic energy generated by an electrical RF pulse.
Lastly, U.S. Pat. No. 4,513,384, issued Apr. 23, 1985, discloses the use of a laser and PZ transducer for nondestructively determining the thickness of and defects within thin films deposited on a substrate. Measurement and depth profile determinations are made using a thermal wave detection system.